Is there any chance she could be gravid? It does look like an egg. It may be a fat pad. Females kept by themselves occasionally do lay, so give her something to dig in (like a glad ware container with some coco fiber in it).
I did but her from a pet store but they told me she was a male so she could have been in the tank with males they had ten in one tank is there a good web page I should go to so I can get more Info on egg laying and what not I was not planning to breed so I'm not sure what to do I will add a spot for her to dig thank you so much for your help